Innerspring assemblies are conventionally made from arrays of vertically-oriented coil springs (i.e., the longitudinal axes of the typical helical springs are perpendicular to the innerspring support surface). The springs are arranged in a generally side-by-side arrangement, usually in parallel columns and parallel rows, to form a support surface. To secure the individual spring coils together and form a unitary innerspring assembly, some form of attachment means is normally employed, such as clips or a cross-helical lacing wire. Most commonly, the springs are attached together at their terminal convolutions, i.e., the metal turn at the very top and bottom of the springs. See, for example, Bell, U.S. Pat. No. 2,611,910, and Flesher et al., U.S. Pat. No. 4,726,572. This creates a planar surface over the ends of the coils over which foam and upholstery is laid.
A recently developed new type of coil, as described in commonly assigned U.S. Pat. No. 5,713,088, has a helical coil body with "terminal convolutions" which extend from one or both ends of the coil body. The terminal convolutions are also helical, with a radius less than that of the coil body. These type of coils are secured or laced together in an innerspring by attachment at the coil heads, located between the coil body and terminal convolution. The terminal convolutions are thus free to compress and laterally deflect. One particular advantage of this type of coil is that it provides a dual spring rate, with the terminal convolution providing an initial relatively soft spring force, and then compresses fully upon the body of the coil which provides a relatively firmer spring force. The extent of lateral deflection of the terminal convolutions is perceptible, particularly upon initial loading. Traditional planar type padding laid over the top of the terminal convolutions tends to dampen the advantageous dual spring rate feel of an innerspring constructed with these types of coils.
In most flexible support surfaces such as mattresses and furniture, internal pads are laid over the top supporting surface of innerspring assemblies to provide soft cushioning in addition to the flexible support provided by the springs. One mattress pad/innerspring assembly design described in U.S. Pat. No. 5,327,596 has a foam cushion having individual, unconnected springs imbedded in the foam cushion. The springs are completely encased in preformed cavities in the foam, or screwed into the cushion body. This type of construction is not practical for conventional innerspring assemblies.
In another mattress pad/innerspring assembly design, shown in U.S. Pat. No. 3,145,020, cylindrical recesses are formed in the mattress pad or cushion. The cylindrical recesses are joined through interconnecting channels formed in the mattress pad. The innerspring assembly is formed into an array which corresponds to the cylindrical recesses in the pads and fit into the pads. Annular protuberances extend through the center of the springs. When fully assembled, the innerspring assembly is completely embedded between the two pads. Although these examples provide various combinations of foam with innersprings, they are rather complex, costly to manufacture, and tend to over-dampen the action of the springs. The prior art does not provide a pad which is specially configured or adapted to integrally fit with innerspring assemblies which have springs with free terminal convolutions.